add metadata api

[saber-wang]

Description

@halspang In order to handle conflicts and use grpc, I opened a new merge request.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #883

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Merging #947 (be3029e) into master (37ed498) will increase coverage by 0.30%.
The diff coverage is 100.00%.

❗ Current head be3029e differs from pull request most recent head f8b98ef. Consider uploading reports for the commit f8b98ef to get more accurate results

@@            Coverage Diff             @@
##           master     #947      +/-   ##
==========================================
+ Coverage   69.49%   69.79%   +0.30%     
==========================================
  Files         155      156       +1     
  Lines        5130     5181      +51     
  Branches      554      554              
==========================================
+ Hits         3565     3616      +51     
  Misses       1434     1434              
  Partials      131      131              

Flag	Coverage Δ
net5	69.73% <100.00%> (+0.28%)	⬆️
net6	69.69% <100.00%> (+0.30%)	⬆️
netcoreapp3.1	69.75% <100.00%> (+0.32%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/Dapr.Client/DaprClient.cs	93.61% <ø> (ø)
src/Dapr.Client/DaprClientGrpc.cs	87.19% <100.00%> (+0.46%)	⬆️
src/Dapr.Client/DaprMetadata.cs	100.00% <100.00%> (ø)
src/Dapr.Client/ConfigurationItem.cs	100.00% <0.00%> (ø)

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[BartNetJS]

I'm testing the meta data implementation.
Is it also possible to get the url from an http binding:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
name: myservice
namespace: mynamespace
spec:
type: bindings.http
version: v1
metadata:
- name: url
value: http://some-url:8090

[saber-wang]

@BartNetJS
This information cannot be obtained. The api can refer to this document https://docs.dapr.io/reference/api/metadata_api/.

You can also propose this function in dapr